Process for the preparation of substantially pure cyclo aliphatic diisocyanate stereoisomers

ABSTRACT

The instant invention is directed to a novel process for the separation of substantially pure cycloaliphatic diisocyanate reactive (cis-form) stereoisomers from cycloaliphatic diisocyanate non-reactive (trans-form) stereoisomers comprising reacting cycloaliphatic diisocyanates of the formula ##STR1## where R can be hydrogen or an aliphatic hydrocarbon group having from 1 to 4 carbon atoms, at least one of said R&#39;s being an aliphatic hydrocarbon having from 1 to 4 carbon atoms and wherein the isocyanato groups are both positioned axially or equatorially in the presence of catalysts selected from the group consisting of lead catalysts, tertiary amines, alkali metal hydroxides and sodium methoxide, thereby producing a cyclic nylon-1 type linear polymer having regularly reoccurring bicyclic structural units of the formula ##STR2## precipitating said cyclic nylon-1 type linear polymers, filtering and washing said precipitated cyclic nylon-1 type linear polymers, then decomposing said precipitated polymer using distillation, thereby producing a distillate and collecting said distillate containing a substantially pure monomer consisting of reactive (cis-form) stereoisomers. The instant invention also relates to the novel process outlined above wherein the decomposition by distillation is performed under conditions of reduced pressure.

This application is a division of my copending application Ser. No.008,450 filed Feb. 1, 1979.

BACKGROUND OF THE INVENTION

It is well known that organic isocyanates may be polymerized to highmolecular weight linear organic polymers. Thus, e.g. in U.S. Pat. No.2,965,614, a process is described wherein an isocyanate in which theisocyanate group (or groups) is attached to a carbon atom bearing atleast two hydrogen atoms is treated under anhydrous conditions with analkali metal anionic catalyst at a temperature below about -20° C. in asolvent for the isocyanate and the catalyst. The products are describedas being linear polymers.

Similarly, in U.S. Pat. No. 3,163,624, trimethylene diisocyanate oralkyl and/or aryl substituted trimethylene diisocyanates are treatedwith an alkali metal anionic catalyst at a temperature of from about-20° C. to about -100° C. or lower to produce a linear polymercontaining 6-membered rings.

In U.S. Pat. No. 3,048,566, a high molecular weight synthetic linearpolymer of an organic polyisocyanate having at least two vicinalisocyanate groups is described. The polymer is characterized by arepeating five-membered ring structural unit in which the nitrogen ofone of the isocyanate groups is bonded to the carbon atom of an adjacentisocyanate group. The products are made by polymerizing the isocyanateunder anhydrous conditions at a temperature below about 75° C. Thepolymers may be depolymerized by thermal cracking. Example III of thispatent describes the polymerization of cyclohexane-1,2-diisocyanate. Asimilar polymerization process is found in U.S. Pat. No. 3,450,676.

Finally in Corfield and Crawshaw, Chemical Communications, Vol. 4, pages85-86 (1966), the polymerization of cis 1,3-cyclohexane diisocyanate isdescribed. The process used consists of treating the isocyanate withsodium cyanide in a dimethyl formamide solution at a temperature of from-40° C. to -60° C. The resultant polymer unit is described as ##STR3##

DESCRIPTION OF THE INVENTION

The instant invention is directed to novel heterocyclic nylon-1 typelinear polymers and to the novel method of their manufacture. The novelpolymers herein comprise regularly recurring bicyclic structural unitshaving the general formula: ##STR4## where R can be hydrogen or analiphatic hydrocarbon group of from 1 to 4 carbon atoms, at least one ofsaid R's being an aliphatic hydrocarbon group of from 1 to 4 carbonatoms, and wherein said polymers contain from 2 to 100 of said recurringstructural units. In general, the polymers of the instant invention willhave number average molecular weights of from about 500 to about 35,000.

The novel process herein comprises reacting certain specifiedcycloaliphatic diisocyanates in the presence of specified catalysts at atemperature of from about 50° C. to about 150° C. The isocyanates usefulin the instant invention are generally of the formula: ##STR5## where Ris hydrogen or an aliphatic hydrocarbon group of from 1 to 4 atoms, atleast one of said R's being an aliphatic hydrocarbon of from 1 to 4carbon atoms. Specific useful cycloaliphatic diisocyanates include1-methyl-2,4-diisocyanato-cyclohexane,1-methyl-2,6-diisocyanato-cyclohexane, 1-ethyl-2,4- and2,6-diisocyanato-cyclohexane, 1,3-dimethyl-2,4- and 2,6-diisocyanatocyclohexane, and mixtures thereof. The presently preferred isocyanatesare 1-methyl-2,4- and -1-methyl-2,6-diisocyanato-cyclohexane andmixtures thereof. Also useful and preferred are mixtures of hydrogenated2,4- and 2,6-toluene diisocyanate. Finally, the isocyanato groups mustbe positioned both axial or both equatorial since it has been found thatthe reaction will not proceed when one is axial and the otherequatorial.

The catalysts useful in the instant invention include lead catalystssuch as lead octoate, lead laurate, lead oleate, lead napthenate, andthe like; tertiary amines such as dimethylaminoethanol, triethylenediamine, N,N,N',N'-tetramethylethylene diamine, N,N-dibutyl urea, andthe like; alkali metal hydroxides such as sodium hydroxide, potassiumhydroxide and the like; and sodium methoxide.

It is generally preferred to conduct the polymerization in the presenceof an inert solvent. For this purpose, useful solvents includehydrocarbons such as xylene, halogenated aliphatic or aromatichydrocarbons such as methylene chloride, chloroform, trichloroethylene,chlorinated benzene, ketones such as acetone, methyl ethyl ketone,diethylketone, esters such as ethyl acetate, butyl acetate, glycolmonomethyl ether acetate, glycol monoethyl ether acetate and ethers suchas tetrahydrofuran and dioxane and mixtures thereof. The presentlypreferred solvent is xylene.

In general, the components are merely mixed together and heated to fromabout 50° C. to about 150° C. for from 5 minutes to about 96 hours. Thecatalyst is generally used in amounts ranging from 0.001 to 1 percent byweight based on the amount of diisocyanate.

Inasmuch as the products of the instant invention de-polymerizequantitatively to the monomeric form at about 230° C., they areeminently suitable for use as splitters or camouflaged isocyanates.

The invention is further illustrated, but is not intended to be limitedby the following examples in which all parts and percentages are byweight unless otherwise specified.

EXAMPLES EXAMPLE 1

A mixture of 80% 2,4- and 20% 2,6-toluene diamine was hydrogenated tothe cyclohexyl form.

This was done by melting 1,200 g of 80/20 TDA at 110° C. and slurring 50g of activated charcoal into the TDA for about 10 minutes. The moltenTDA was filtered through a celite bed on a steam heated Buchner funnel.1,000 g of the filtrate were hydrogenated in a 1-gallon autoclave at4,500 psig for 4 hours. The autoclave was then cooled and depressurized.The liquid product was then filtered.

The three major stereoisomers present were:

    ______________________________________                                        (e = equatorial, a = axial):                                                  (x) 4-e-NH.sub.2 ; 2-e-NH.sub.2 49.4%                                         (y) 4-a-NH.sub.2 ; 2-e-NH.sub.2 17.3%                                                               78.7%                                                   (z) 6-e-NH.sub.2 ; 2-e-NH.sub.2 12.0%                                         ______________________________________                                    

Note that isomers in which both NH₂ are equatorial or axial (cisstructure) total 61.4%. This mixture of amines was phosgenated in knownmanner to yield the corresponding isocyanate (46.6% NCO) which was usedin most of the following examples.

The formation of the claimed cyclic Nylon-1 structure in the followingExamples (2-12) was confirmed by IR, which showed a distinctly differentspectrum than was obtained by linear Nylon-1 or isocyanurate structures.

EXAMPLE 2

300 g of the isocyanate of Example 1 and 4.5 g of lead octoate wereplaced in a 500 ml 3-necked flask padded with N₂ and heated at 120°-145°C. After about one hour the viscosity had increased to the point where200 g xylene were added. At this point the NCO content of the solutionwas 11.4%. Heating was continued at 110°-125° C. for an additional 4hours, after which the NCO content was still 11.4%, indicating that thedesired reaction had occurred within the first hour. The monomer contentof this solution was found to be 25%, which would in itself account for0.25×46.6% or 11.6% of the unreacted NCO, indicating that the polymermust be fairly high in molecular weight and essentially low in NCOterminal groups. The 25% monomer content of the solution corresponds to41.6% unreacted monomer based on the original isocyanate charged,indicating that 41.6% of the isomers present in the isocyanate did notpolymerize under these conditions.

The xylene solution was diluted with an additional 500 ml xylene andthen 1,500 ml heptane were slowly added with stirring to precipitate thepolymer. The polymer was filtered, washed with 5,000 ml heptane anddried in a 100° C. vacuum oven (A). The combined filtrate and washingswere concentrated and distilled to yield a distillate (B) and a potresidue (C):

    ______________________________________                                                   2-A     173.5 g  57.8%  (polymer)                                             2-B      94.0 g  31.3%                                                                                 (monomer)                                            2-C      15.0 g   5.0%                                             Total recovered    282.5 g  94.1%                                             ______________________________________                                    

Subsequent examination of the 2-A polymer revealed the following:

    ______________________________________                                        Melting point (by differential                                                thermal analysis - DTA)                                                                         253° C.                                              Decomposition temperature                                                     (by DTA)          about 290° C.                                        Molecular weight  5,300 (the NCO content if                                                     terminated with NCO                                                           groups 1.6%)                                                Actual % NCO found                                                                              0.4%                                                        Monomer content   <0.1%                                                       ______________________________________                                    

The 2-A polymer was readily soluble (33% solution) in methylenechloride, xylene and diethyl benzene, but essentially insoluble intriethylbenzene, heptane or hexane.

EXAMPLE 3

5 g of polymer 2-A were placed in micro distillation equipment andheated to a pot temperature of about 230° C. under 2 mm pressure. Theproduct decomposed and distilled over at a head temperature of about132° C. This was repeated four more times and the five distillates (3-A)combined. Examination of the distillate revealed an NCO content of 46.0%and IR spectrum very similar to that of hydrogenated TDI, demonstrating:

(1) that the polymer could be broken down by vacuum distillation intothe original monomer, and

(2) this process could be used to separate the reactive stereoisomers(ee and aa), sample 2-A, from the non-reactive (e,a and a,e), sample2-B.

EXAMPLE 4

Since the essentially NCO free polymer was capable of regeneratingmonomer at elevated temperature, it should be possible to use thepolymer as a "camouflaged" isocyanate or isocyanate "splitter".

3.4 g of Multron R-12 (available from Mobay Chemical Corporation), abranched liquid polyester prepared from 1,3-butanediol,trimethylolpropane, adipic acid and maleic acid so as to have an OHnumber of 165, was mixed with 1.0 g of polymer 2-A and 4.0 g xylene. Theresulting solution was cast onto an aluminum sheet. The solventevaporated and the lacquer film baked under various conditions.

    ______________________________________                                        15 minutes at 130° C.                                                  25 minutes at 150° C.                                                                       No significant changes                                   15 minutes at 175° C.                                                  30 minutes at 200° C.                                                                       A hard, tough film was produced.                         ______________________________________                                    

This demonstrates that the 2-A polymer can react with OH-containingmaterials only at elevated temperatures.

EXAMPLE 5

1.76 g of a diamine H₂ N--C₂ H₄ --O--C₂ H₄ --O--C₂ H₄ --NH₂ and 2.0 g ofpolymer 2-A are dissolved in 8.0 g of xylene and cast onto an aluminumsheet. After evaporation of the xylene, the film exists as a viscouslayer. Baking for 15 minutes at 175° C. causes a darkening and anincrease in viscosity. Continued baking for 15 minutes at 200° C. causesthe liquid film to turn to a dark, tacky thermoplastic solid at 200° C.,which turns to a hard tough film upon cooling to room temperature.

EXAMPLE 6

A sample of hydrogenated TDI (46.4% NCO) was prepared from hydrogenatedamine. 100 g of the isocyanate and 0.7 g of a 50% solution of leadoctoate in xylene were heated in a flask at 125°-140° C. Within one houra pronounced increase in viscosity occurred, so 66.7 g of xylene wereadded. The NCO content of this solution was 11.1%, equivalent to18.5%-NCO on a solvent-free basis indicating that 18.5÷46.4 or 39.8% ofthe NCO was nonreactive (compared to 41.6% in Example 2).

EXAMPLE 7

Same as Example 6 except 0.2 g of lead acetate were used. The xylene wasadded after 3 hours of heating at 115°-135° C., and the NCO content ofthe resulting solution was 11.6% NCO (compared to 11.1% in Example 6).

EXAMPLE 8

A sample of TDA was hydrogenated, then phosgenated to yield adiisocyanate of 45.6% NCO content. 50 g were placed in a 3-necked flaskwith 0.5 g lead octoate and heated at 110°-120° C. After 30 minutes theviscosity increased and 50 g of xylene were added. The NCO content ofthe resulting solution was 13.0%. Heating was resumed for 3 more hours,after which the NCO content was 10.1%. This corresponds to 20.2% NCO ona xylene free basis, signifying that 20.2÷45.6 or 44.3% of the originalNCO remain unreacted.

The solution was diluted with 100 ml xylene and 2,000 ml of hexane wereslowly added with stirring to precipitate the polymer, which wasfiltered, washed and dried. The yield was 26 g, a yield of 52% based onthe original isocyanate charged.

EXAMPLE 9

100 g of the isocyanate of Example 1 and 0.1 g NaOCH₃ were placed in a3-necked flask and heated at 110°-145° C. Within 30 minutes theviscosity increased and 67 g of xylene were added. The NCO content ofthe resulting solution was 11.4%, and IR spectra indicated the samecyclic Nylon-1 structure obtained in Examples 2, 6, 7 and 8.

EXAMPLE 10

5 g portions of various isocyanates were sealed into dry 16 ml vialsalong with 0.07 g of lead octoate and heated in a 75° C. oven for 4hours:

    ______________________________________                                                      Appearance After                                                Isocyanate Used                                                                             4 hours at 75° C.                                                                   IR Spectra                                         ______________________________________                                        Ex 1          very viscous Nylon-1 structure                                  Ex 2-B        no change    isocyanate; no                                                                reaction                                           Cyclohexyl isocyanate                                                                       no change    isocyanate; no                                                                reaction                                           1,6-hexane diisocyanate                                                                     low viscosity                                                                              some isocyanurate                                  ______________________________________                                    

This demonstrates that only certain isomers present in Example 1 arecapable of forming the peculiar cyclic Nylon-1 structure. The unreactivedistillate obtained in Example 2-B was still non-reactive, as was purecyclohexyl isocyanate. A typical alkyl isocyanate forms conventionalisocyanurate rather than the Nylon-1 structure.

EXAMPLE 11

1,000 g of the isocyanate of Example 1 and 5 g of dimethyl aminoethanolwere placed in a 3-necked flask and heated for two hours at 125° C. Atthe end of the day, the material was allowed to stand overnight at roomtemperature. The next morning an additional 5 g of catalyst were addedand heating resumed. After two more hours, the contents were observed tobe dark colored and viscous. The NCO content was 24.4%, indicating thatonly 46.7÷24.4 or 52% of the original NCO groups remained unreacted.

EXAMPLE 12

200 g of hydrogenated 2,4-tolylene diisocyanate were dissolved in 200 gof xylene and reacted in the presence of 0.15 g of DABCO TMR-2 (atertiary amine manufactured by Air Products). After stirring for twohours at room temperature, no reaction was noticeable. The mixture wasthen heated from about 70° to 102° C. for about 5 hours and then asample was tested for NCO content. The NCO content was 44.5%. About 0.3g of DABCO TMR-2 was added at about 80° C. The mixture was then allowedto cool overnight at room temperature. A sample was taken in the morningand the NCO content was 32.64%. The mixture was then treated at about77°-96° C. for 6 hours. The final sample at the end of this time had anNCO content of 30.55%.

What is claimed is:
 1. A process for the separation of substantiallypure cycloaliphatic diisocyanate reactive (cis-form) stereoisomers fromcycloaliphatic diisocyanate non-reactive (transform) stereoisomerscomprising the steps of:(a) reacting:(1) cycloaliphatic diisocyanates ofthe formula ##STR6## where R is hydrogen or an aliphatic hydrocarbongroup having from 1 to 4 carbon atoms, at least one of said R's being analiphatic hydrocarbon having from 1 to 4 carbon atoms and wherein theisocyanato groups are both positioned axially or equatorially in thepresence of (2) catalysts selected from the group consisting of leadcatalysts, tertiary amines, alkali metal hydroxides, and sodiummethoxide thereby producing a cyclic nylon-1 type linear polymer havingregularly reoccuring bicyclic structural units of the formula ##STR7##(b) precipitating said cyclic nylon-1 type linear polymers; (c)filtering and washing said precipitated cyclic nylon-1 type linearpolymers; (d) decomposing said precipitated polymer using distillationthereby producing a distillate; (e) collecting said distillatecontaining a substantially pure monomer consisting of reactive(cis-form) stereoisomers.
 2. A process as claimed in claim 1, whereinstep (d) is performed under conditions of reduced pressure.